Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, FIG. 1 depicts a conventional magnetic tunneling junction (MTJ) 10 as it may be used in a conventional STT-MRAM. The conventional MTJ 10 typically resides on a substrate 12. A bottom contact 14 and top contact 22 may be used to drive current through the conventional MTJ 10. The conventional MTJ, uses conventional seed layer(s) (not shown), may include capping layers (not shown) and may include a conventional antiferromagnetic (AFM) layer (not shown). The conventional magnetic junction 10 includes a conventional reference layer 16, a conventional tunneling barrier layer 18, and a conventional free layer 20. Also shown is top contact 22. Conventional bottom contact 14 and top contact 22 are used in driving the current in a current-perpendicular-to-plane (CPP) direction.
The conventional reference layer 16 and the conventional free layer 20 are magnetic. The magnetization 17 of the conventional reference layer 16 is fixed, or pinned, in a particular direction. The conventional reference layer 16 may be a multilayer such as a synthetic antiferromagnetic (SAF) layer including magnetic layers antiferromagnetically coupled through thin conductive layers, such as Ru. The conventional free layer 20 has a changeable magnetization 21. Although depicted as a simple layer, the conventional free layer 20 may also include multiple layers. The conventional reference layer 16 and free layer 20 may have their magnetizations 17 and 21, respectively oriented perpendicular to the plane of the layers.
In order to achieve perpendicular magnetic moments 17 and 21 and high magnetoresistance, various structures have been proposed. For example, alloys such as CoFeB and/or FeB may be used in the free layer 20 or reference layer 16. The inclusion of B allows the alloy to be amorphous as deposited. During fabrication, the reference layer 16 and/or free layer 20 generally undergoes one or more anneals. As a result, the boron tends to diffuse, leaving the CoFeB and FeB better crystallized and boron poor. In order to maintain the performance, the boron is desired to be removed not only from the layer being crystallized, but also the conventional magnetic junction 10. Some methods of doing so may damage the magnetic junction. As a result, the magnetoresistance of the magnetic junction 10 may be adversely affected. Accordingly, what is needed is a method and system that may improve the performance of the spin transfer torque based memories. The method and system described herein address such a need.